Viral culture or immunofluorescent staining may be used to differentiate herpes simplex from herpes zoster in cases that are difficult to distinguish clinically.

Antibodies to herpes zoster can be measured. A 4-fold increase has been used to support the diagnosis of subclinical herpes zoster (zoster sine herpete). However, a rising titer secondary to viral exposure rather than reactivation cannot be ruled out.

Imaging Studies

MRI lesions attributable to HZ were seen in the brain stem and cervical cord in 9 patients (56%).

At 3 months after onset of HZ, 5 patients (56%) with an abnormal MRI had developed PHN.

Of the 7 patients who had no HZ-related lesions on MRI, none had residual pain.

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Histologic Findings

Although HZ symptoms may be confined to a few sensory dermatomes, pathological changes may be more widespread. Affected ganglia of the spinal or cranial nerve roots are swollen and inflamed with a primarily lymphocytic reaction. Some ganglion cells are swollen while others are degenerated.

Inflammation extends into the meninges and root entry zone and may be present in the ventral horn and perivascular space of the spinal cord. Pathological changes in the brain stem are similar to those in the spinal root and spinal cord. In the months following infection, fibrosis occurs in the ganglia, peripheral nerve, and nerve root. Degeneration occurs in the ipsilateral posterior column.